In the manufacturing process of the hot-rolled silicon steel, it's easy for various defects to occur in the course of rolling on the edges where stress is concentrated and temperature change is very dramatic, which thus influences the overall quality of the silicon steel, reduces the yield of products and further lowers the productivity effect. Specifically, the edge seam defect is one of the common edge defects of the hot-rolled silicon steel. Researches show that the edges and corners of the slab are always in a low temperature and high stress and strain status in the course of rolling; in the course of horizontal rolling, the inward frictional force of the roller on the rolled piece subjects the corner metal to the action of the intensive tensile stress, which finally flows to the upper surface of the rolled piece; with the progress of the post-horizontal rolling passes, the newly-formed boundaries push the original boundaries to move in a direction far away from the edges of the slab, and the intensive tensile stress status may induce the occurrence of the “black line” defect.
At present, there have been various reports on improving the said edge defects. For example, the patent literature 1 discloses a continuous casting crystallizer, on which the side wall of the short slab is designed into the circular arc shape and the four corners are designed into round corners, so as to achieve the side face of casting slab with circular arc round corners, prevent the occurrence of edges or corners flanging in the hot rolling process of the slab, avoid the rapid cooling of edges and corners and thus eliminate longitudinal linear black line and peeling-off defects. The patent literature 2 discloses a method by which the high surface quality of the silicon steel may be obtained through controlling the temperature gradients between the slab surface and a location at a certain depth of the silicon steel during the course of rough rolling and finishing rolling. Literature 3 adopts the grooved roll and the convex-type slab sizing press (SSP) module for the concave molding of the slab's side face to avoid the occurrence of defects, and has certain disadvantages: the grooved roll may easily cause serious scratches, and the convex-type SSP module may lead to unstable reduction and thus result in unstable rolling. Literatures 4 and 5 studied the basic flow rule of the metal in the edges and corners of the slab in the process of vertical-horizontal rolling process during rough rolling by the approach of numerical simulation calculation, and made a calculation with respect to the rule of the influence of various vertical roll shapes on the flow of the metal in the edges and corners of the rolled piece. However, the results of the research have not gone through production verification, and also belong to an improved method about reduction by the vertical roll during rough rolling. Literature 6 redesigns and modifies the vertical roll of the rough rolling mill to eliminate mechanical damages in the production process. Besides, in the production practice, the SSP module used has also been modified in some cases for the concave forming of the slab's side face, however, restrained by the unstable contact between the convex-type SSP module and the slab in the course of rolling, it leads to asymmetric metal flow on the two sides and makes it difficult to control the slab shape in subsequent rough rolling.
However, the literatures available so far are all concerned with the simulative calculation and actual improvement of the influence of the vertical roll and rolling piece shapes of rough rolling on the distance between a defect and the edges (edge distance). At present, there are no reports on eliminating and improving defects through changing the temperature of the rolled piece, particularly through changing the cross-sectional temperature of the rolled piece.
Existing technical literatures:    1. Chinese utility model patent ZL200720067413.7    2. U.S. Pat. No. 5,572,892A    3. YAMAGUCHI HARUO, KUSABA YOSHIAKI, YAMADA TAKEO, Techniques for the Control of Edge Crack Defects of Stainless Steel Sheets, Foreign Steel, 1996(12):48-52.    4. Xiong Shangwu, J. M. C. Rodrigues, P. A. F. Martins. Three-dimensional modelling of the vertical-horizontal rolling process [J], Finite Elements in Analysis and Design, 2003, 39:1023-1037.    5. Xiong Shangwu, Liu Xianghua, Wang Guodong, et al., Three-dimensional thermo-mechanical finite element simulation of the vertical-horizontal rolling process [J]. Journal of Materials Processing Technology, 2011, 11:89-97.    6. Gao Wenfang, Yan Zhengguo, Song Ping, Rao Kewei, Chen Fangwu, Kong Yongjiang, Research on the Linear Defects along the Edges of Shadow Mask and Chassis Cold-rolled Sheets [J], Steelmaking, 2003, 19(1).